Thermal diffusivity of a substance is
Directly proportional to thermal conductivity
Inversely proportional to density of substance
Inversely proportional to specific heat
All of the above
Correct Answer :
D. All of the above
Related Questions
Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
Cold body to hot body
Hot body to cold body
Smaller body to larger body
Larger body to smaller body
Thermal conductivity of wood depends on
Moisture
Density
Temperature
All of the above
The transfer of heat by molecular collision is known as
Conduction
Convection
Radiation
None of these
Metals are good conductors of heat because
Their atoms collide frequently
Their atoms are relatively far apart
They contain free electrons
They have high density
According to Stefan's law, the total radiation from a black body per second per unit area is proportional to
Absolute temperature
T²
T⁵
T
40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
0.45
0.55
0.40
0.75
The natural convection air cooled condensers are used in
Domestic refrigerators
Water coolers
Room air conditioners
All of these
The unit of Stefan-Boltzmann constant is
Watt/mK
Watt/m²K²
Watt/m²K4
Watt/mK²
The unit of overall coefficient of heat transfer is
W/m²K
W/m²
W/mK
W/m
Thermal diffusivity of a substance is
Directly proportional to the thermal conductivity
Inversely proportional to density of substance
Inversely proportional to specific heat
All of the above
Log mean temperature difference in case of counter flow compared to parallel flow will be
Same
More
Less
Depends on other factors
Wiens law states that the wave length corresponding to ________ is proportional to the absolute temperature.
Minimum energy
Maximum energy
Both (A) and (B)
None of these
In counter current flow heat exchanger, the logarithmic temperature difference between the fluids is ________ as compared to parallel flow heat exchanger.
Same
Less
Greater
None of these
Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
1 : 1
2 : 1
1 : 2
4 : 1
The critical thickness of insulation for a sphere is
k/h₀
2k/h₀
h₀/k
h₀/2k
The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body
Move actually
Do not move actually
Affect the intervening medium
Does not affect the intervening medium
The rate of energy transferred by convection to that by conduction is called
Stanton number
Nusselt number
Biot number
Peclet number
Reynolds number is the ratio of
Energy transferred by convection to that by conduction
Kinematic viscosity to thermal diffusivity
Inertia force to viscous force
None of the above
Thermal conductivity of water ________ with rise in temperature.
Remain same
Decreases
Increases
May increase or decrease depending upon temperature
In regenerator type heat exchanger, heat transfer takes place by
Direct mixing of hot and cold fluids
A complete separation between hot and cold fluids
Flow of hot and cold fluids alternately over a surface
Generation of heat again and again
A steam pipe is to be insulated by two insulating materials put over each other. For best results
Better insulation should be put over pipe and better one over it
Inferior insulation should be put over pipe and better one over it
Both may be put in any order
Whether to put inferior OIL over pipe or the better one would depend on steam temperature
Heat is closely related with
Liquids
Energy
Temperature
Entropy
When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by
Conduction
Convection
Radiation
Conduction and convection
The automobile radiator is a heat exchanger of
Parallel flow type
Counter flow type
Cross flow type
Regenerator type
The critical temperature is the temperature
Below which a gas does not obey gas laws
Above which a gas may explode
Below which a gas is always liquefied
Above which a gas will never liquefied
Fourier's law of heat conduction is valid for
One dimensional cases only
Two dimensional cases only
Three dimensional cases only
Regular surfaces having non-uniform temperature gradients
The expression Q = ρ AT4 is called
Fourier equation
Stefan-Boltzmann equation
Newton Reichmann equation
Joseph-Stefan equation
Thermal diffusivity is a
Function of temperature
Physical property of a substance
Dimensionless parameter
All of these
The value of the wavelength for maximum emissive power is given by
Wien's law
Planck's law
Stefan's law
Fourier's law
Thermal conductivity of solid metals with rise in temperature normally
Increases
Decreases
Remain constant
May increase or decrease depending on temperature